Materials and Catalysts for Pollutants and CO₂ Capture and Transformation

Topic Information

Dear Colleagues,

This is call for papers that focus on the topic of materials and catalysts that are capable of capturing or transforming pollutants and CO₂; studies that explore process analyses and profitability are also very welcome. Nowadays, the concentration of pollutants in the atmosphere, soil and water is increasing due to human activity, causing a negative environmental impact in many ecosystems. Different approaches to environmental remediation that could mitigate this phenomenon include three steps: reducing emissions, capturing pollutants from the ecosystem and converting them to valuable chemicals. A profitable technology for CO₂ and pollutants conversion to valuable products would accelerate industrial implementation. That is why an particular emphasis must be given to this applicability, where catalyst and materials play a crucial role.

During last decade, many procedures/technologies have been developed using catalysts, which have led to a wide range of products, from simple molecules such as H₂ to very complex hydrocarbons. All of these hydrocarbons have industrial applications, and thus they promote the development of a circular economy. Similar to a circular economy, the development of active materials and catalysts designed to be easily reused as many times as possible, and then recycled after their active life, is one of the actual greatest challenges in this field. In addition, they should be obtained from a very abundant source.

However, since not only one procedure will be able to solve this contamination problem, several procedures that help to restore desirable levels of clean air would be also consideredIn the short term, there is a particular interest in converting CO₂ to fuels or energy vectors, as this technology would recycle the CO₂ emitted by fossil-fuel-based industries and activities, considerably reducing their carbon footprint. The aim of this Special Issue is to cover the research trends on materials and catalysts for the capture and conversion of CO₂ and pollutants. Full papers, short communications and reviews in this field are welcomed. Mini-reviews with an overview on state-of-the-art innovations with the future perspectives and trends will be also considered.

Dr. Vicente Montes
Dr. Rafael Estevez
Dr. Manuel Checa
Topic Editors

Keywords

Participating Journals

Journal Name	Impact Factor	CiteScore	Launched Year	First Decision (median)	APC
Catalysts catalysts	3.8	6.8	2011	12.9 Days	CHF 2200
ChemEngineering ChemEngineering	2.8	4.0	2017	29.6 Days	CHF 1600
Energies energies	3.0	6.2	2008	17.5 Days	CHF 2600
Materials materials	3.1	5.8	2008	15.5 Days	CHF 2600
Nanomaterials nanomaterials	4.4	8.5	2010	13.8 Days	CHF 2900

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Published Papers (16 papers)

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15 pages, 4565 KiB  

Open AccessArticle

Synthesizing and Characterizing a Mesoporous Silica Adsorbent for Post-Combustion CO₂ Capture in a Fixed-Bed System

by Hind F. Hasan, Farah T. Al-Sudani, Talib M. Albayati, Issam K. Salih, Hamed N. Harharah, Hasan Sh. Majdi, Noori M. Cata Saady, Sohrab Zendehboudi and Abdelfattah Amari

Catalysts 2023, 13(9), 1267; https://doi.org/10.3390/catal13091267 - 2 Sep 2023

Cited by 5 | Viewed by 1803 | Correction

Abstract

MCM-41, a mesoporous silica with a high surface area and hexagonal structure, was synthesized, and commercial nano-silicon dioxide (SiO₂) was used as a solid adsorbed in post-combustion CO₂ capture. The CO₂ adsorption experiments were conducted in a fixed-bed adsorption [...] Read more.

MCM-41, a mesoporous silica with a high surface area and hexagonal structure, was synthesized, and commercial nano-silicon dioxide (SiO₂) was used as a solid adsorbed in post-combustion CO₂ capture. The CO₂ adsorption experiments were conducted in a fixed-bed adsorption system using 5–15 vol.% CO₂/N₂ at a flow rate of 100 mL/min at varying temperatures (20–80 °C) and atmospheric pressure. Analyses (X-ray diffraction, nitrogen adsorption-desorption isotherms, Fourier-transform infrared spectroscopy, and transmission electron microscopy (TEM)) revealed that the synthesized MCM-41 has mesoporous characteristics: a high surface area and large pore volumes. The CO₂ adsorption capacity of MCM-41 and commercial nano-SiO₂ increased considerably with increasing CO₂ concentration and temperature, peaking at 60 °C. Below 60 °C, dynamics rather than thermodynamics governed the adsorption. Increasing the temperature from 60 to 80 °C decreased the adsorption capacity, and the reaction became thermodynamically dominant. Additionally, compared with commercial nano-SiO₂, the MCM-41 sorbent demonstrated superior regenerability and thermal stability. Full article

(This article belongs to the Topic Materials and Catalysts for Pollutants and CO₂ Capture and Transformation)

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Figure 1

Figure 1
<p>X-ray diffraction patterns of MCM-41: (<b>a</b>)—before and (<b>b</b>)—after CO₂ adsorption.</p> Full article ">Figure 2
<p>X-ray diffraction patterns of SiO₂: (<b>a</b>)—before and (<b>b</b>)—after CO₂ adsorption.</p> Full article ">Figure 3
<p>EDX—SEM of (<b>a</b>)—Fresh MCM-41, (<b>b</b>)—MCM-41 after adsorption, (<b>c</b>)—Fresh SiO₂, and (<b>d</b>)—SiO₂ after adsorption.</p> Full article ">Figure 3 Cont.
<p>EDX—SEM of (<b>a</b>)—Fresh MCM-41, (<b>b</b>)—MCM-41 after adsorption, (<b>c</b>)—Fresh SiO₂, and (<b>d</b>)—SiO₂ after adsorption.</p> Full article ">Figure 4
<p>FT—IR spectra of (<b>a</b>)—Fresh MCM-41, and (<b>b</b>)—MCM-41 after adsorption.</p> Full article ">Figure 5
<p>FT—IR spectra of SiO₂ (<b>a</b>)—Fresh SiO₂, and (<b>b</b>)—SiO₂ after adsorption.</p> Full article ">Figure 6
<p>TGA analysis for (<b>a</b>)—MCM-41 and (<b>b</b>)—nano-SiO₂.</p> Full article ">Figure 7
<p>TEM images for (<b>a</b>)—MCM-41 and (<b>b</b>)—nano-SiO_2.</p> Full article ">Figure 8
<p>Breakthrough profile of CO₂ adsorption via (<b>a</b>)—MCM-41 and (<b>b</b>)—Nano-SiO₂.</p> Full article ">Figure 9
<p>Cyclic CO₂ adsorption capacity of the MCM-41 and commercial nanoparticle SiO₂.</p> Full article ">Figure 10
<p>Synthesis steps for MCM-41.</p> Full article ">Figure 11
<p>Experimental set-up for the CO₂ adsorption-desorption.</p> Full article ">

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Supplementary material:
Supplementary File 1 (ZIP, 2623 KiB)

23 pages, 4518 KiB  

Open AccessArticle

Enhancement of Photocatalytic Activity and Microstructural Growth of Cobalt-Substituted Ba_1−xCo_xTiO₃ {x = 0, …, 1} Heterostructure

by Sana Jebali, Mahdi Meftah, Chadha Mejri, Abdesslem Ben Haj Amara and Walid Oueslati

ChemEngineering 2023, 7(3), 43; https://doi.org/10.3390/chemengineering7030043 - 1 May 2023

Cited by 4 | Viewed by 3117

Abstract

The photocatalytic degradation process and absorption kinetics of the aqueous solution of the Cibacron Brilliant Yellow 3G-P dye (Y) were investigated under UV-Vis light. Pure barium titanate BaTiO₃ (BT) and cobalt ion-substituted barium Ba_1−xCo_xTiO₃ (x = 0, [...] Read more.

The photocatalytic degradation process and absorption kinetics of the aqueous solution of the Cibacron Brilliant Yellow 3G-P dye (Y) were investigated under UV-Vis light. Pure barium titanate BaTiO₃ (BT) and cobalt ion-substituted barium Ba_1−xCo_xTiO₃ (x = 0, …, 1) nano-compound powders (BCT) were synthesized using the sol–gel method and colloidal solution destabilization, and utilized as photocatalysts. The powder X-ray diffraction (PXRD) crystal structure analysis of the BT nanoparticles (NPs) revealed a prominent reflection corresponding to the perovskite structure. However, impurities and secondary phase distributions were qualitatively identified in the PXRD patterns for x ≥ 0.2 of cobalt substitution rate. Rietveld refinements of the PXRD data showed that the BCT nano-compound series undergoes a transition from perovskite structure to isomorphous ilmenite-type rhombohedral CoTiO₃ (CT) ceramic. The nanoparticles produced displayed robust chemical interactions, according to a Fourier transform infrared spectroscopy (FTIR) analysis. The BT and BCT nanoparticles had secondary hexagonal phases that matched the PXRD results and small aggregated, more spherically shaped particles with sizes ranging from 30 to 114 nm, according to transmission electron microscopy (TEM). Following a thorough evaluation of BCT nano-compounds with (x = 0.6), energy-dispersive X-ray (EDX) compositional elemental analysis revealed random distributions of cobalt ions. Through optical analysis of the photoluminescence spectra (PL), the electronic structure, charge carriers, defects, and energy transfer mechanisms of the compounds were examined. Due to the cobalt ions being present in the BT lattice, the UV-visible absorption spectra of BCT showed a little red-shift in the absorption curves when compared to pure BT samples. The electrical and optical characteristics of materials, such as their photon absorption coefficient, can be gathered from their UV-visible spectra. The photocatalytic reaction is brought about by the electron–hole pairs produced by this absorption. The estimated band gap energies of the examined compounds, which are in the range of 3.79 to 2.89 eV, are intriguing and require more investigation into their potential as UV photocatalysts. These nano-ceramics might be able to handle issues with pollution and impurities, such as the breakdown of organic contaminants and the production of hydrogen from water. Full article

(This article belongs to the Topic Materials and Catalysts for Pollutants and CO₂ Capture and Transformation)

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Figure 1
<p>Characteristic parts of PXRD patterns of Ba_(1−x)Co_xTiO₃ (x = {0, …, 1}) Ba/Co-substituted barium titanate.</p> Full article ">Figure 2
<p>Results of Rietveld refinement of BaTiO₃ structures. Short vertical bars indicate the positions of diffraction maxima in the major tetragonal phase.</p> Full article ">Figure 3
<p>FTIR spectra of Ba/Co-substituted barium titanate samples.</p> Full article ">Figure 4
<p>(<b>a</b>) TEM micrographs and high-resolution images for Ba_1−xCo_xTiO₃ sample with (x = 0.6). EDX spectrum of: (<b>b</b>) pure BT and (<b>c</b>) Ba_0.4Co_0.6TiO₃ (x = 0.6) nano-heterostructure.</p> Full article ">Figure 4 Cont.
<p>(<b>a</b>) TEM micrographs and high-resolution images for Ba_1−xCo_xTiO₃ sample with (x = 0.6). EDX spectrum of: (<b>b</b>) pure BT and (<b>c</b>) Ba_0.4Co_0.6TiO₃ (x = 0.6) nano-heterostructure.</p> Full article ">Figure 5
<p>(<b>a</b>) UV-Vis absorption spectral of synthesized BCT nanoparticles (<b>b</b>) Photoluminescence spectra of all BCT nanoparticles.</p> Full article ">Figure 6
<p>(<b>a</b>) UV-Vis DRS spectra of Ba_0.4Co_0.6TiO₃ solid material for optical band-gap determination and (<b>b</b>) variation of the gap energy as a function of the cobalt substitution rate.</p> Full article ">Figure 6 Cont.
<p>(<b>a</b>) UV-Vis DRS spectra of Ba_0.4Co_0.6TiO₃ solid material for optical band-gap determination and (<b>b</b>) variation of the gap energy as a function of the cobalt substitution rate.</p> Full article ">Figure 7
<p>(<b>a</b>) Photocatalytic degradation rate of CBY3G-P dye over Ba_1−xCo_xTiO₃ NPs as catalysis under 180 min of irradiation and (<b>b</b>) correlation graph showing the variation of photocatalytic degradation of the CBY3G-P as function of cobalt substitution rate.</p> Full article ">Figure 8
<p>Schematic ELD of Ba_0.4Co_0.6TiO₃ with respect to potential for the generation of (O₂•−) (E°(OH/H₂O)) and O₂•− (EO₂/O₂•−) radicals.</p> Full article ">

25 pages, 3973 KiB  

Open AccessFeature PaperArticle

CO₂ Methanation over Nickel Catalysts: Support Effects Investigated through Specific Activity and Operando IR Spectroscopy Measurements

by Vigni V. González-Rangulan, Inés Reyero, Fernando Bimbela, Francisca Romero-Sarria, Marco Daturi and Luis M. Gandía

Catalysts 2023, 13(2), 448; https://doi.org/10.3390/catal13020448 - 20 Feb 2023

Cited by 20 | Viewed by 4763

Abstract

Renewed interest in CO₂ methanation is due to its role within the framework of the Power-to-Methane processes. While the use of nickel-based catalysts for CO₂ methanation is well stablished, the support is being subjected to thorough research due to its complex [...] Read more.

Renewed interest in CO₂ methanation is due to its role within the framework of the Power-to-Methane processes. While the use of nickel-based catalysts for CO₂ methanation is well stablished, the support is being subjected to thorough research due to its complex effects. The objective of this work was the study of the influence of the support with a series of catalysts supported on alumina, ceria, ceria–zirconia, and titania. Catalysts’ performance has been kinetically and spectroscopically evaluated over a wide range of temperatures (150–500 °C). The main results have shown remarkable differences among the catalysts as concerns Ni dispersion, metallic precursor reducibility, basic properties, and catalytic activity. Operando infrared spectroscopy measurements have evidenced the presence of almost the same type of adsorbed species during the course of the reaction, but with different relative intensities. The results indicate that using as support of Ni a reducible metal oxide that is capable of developing the basicity associated with medium-strength basic sites and a suitable balance between metallic sites and centers linked to the support leads to high CO₂ methanation activity. In addition, the results obtained by operando FTIR spectroscopy suggest that CO₂ methanation follows the formate pathway over the catalysts under consideration. Full article

(This article belongs to the Topic Materials and Catalysts for Pollutants and CO₂ Capture and Transformation)

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Figure 1

Figure 1
<p>XRD patterns of the calcined supported Ni catalysts. Crystalline phases identified: (○) NiO, (▽) γ-Al₂O₃, (□) CeO₂, (◇) (Zr_0.88Ce_0.12)O₂, (×) ZrO₂ baddeleyite, (◆) TiO₂ anatase, and (●) TiO₂ rutile.</p> Full article ">Figure 2
<p>H₂-TPR profiles of the calcined supported nickel catalysts.</p> Full article ">Figure 3
<p>CO₂-TPD profiles of the supported nickel catalysts freshly reduced at 500 °C.</p> Full article ">Figure 4
<p>Evolution with reaction temperature of the CO₂ conversion (<b>a</b>), CH₄ yield (<b>b</b>), and CO yield (<b>c</b>) in methanation experiments conducted at space velocity of 12 N L CO₂/(g_cat.·h) and H₂/CO₂ molar ratio of 4. Dashed line in (<b>a</b>) corresponds to the calculated CO₂ equilibrium conversions.</p> Full article ">Figure 5
<p>Methane formation rates expressed per g of catalyst (<b>a</b>), g of Ni (<b>b</b>), and m² of Ni (<b>c</b>), as obtained from experiments conducted at the temperatures indicated, atmospheric pressure, and H₂/CO₂ molar ratio in the reactor feed of 4. Arrhenius plots based on the methane formation rates normalized to the Ni metallic area (<b>d</b>).</p> Full article ">Figure 6
<p>Turnover frequencies of CH₄ formation as functions of the reaction temperature (<b>a</b>). Mean metallic Ni particle size derived from CO chemisorption measurements (<b>b</b>).</p> Full article ">Figure 7
<p>Operando FTIR spectra for CO₂ methanation over the Ni/Al catalyst. Species identification: HC (hydrogen carbonate), MC (monodentate carbonate), BC (bidentate carbonate), OC (organic carbon), F (formate), M (methoxy), FO (formaldehyde).</p> Full article ">Figure 8
<p>Operando FTIR spectra for CO₂ methanation over the Ni/Ce catalyst. Species identification: HC (hydrogen carbonate), MC (monodentate carbonate), BC (bidentate carbonate), PC (polydentate carbonate), F (formate), M (methoxy), FO (formaldehyde), C (carboxylate).</p> Full article ">Figure 9
<p>Operando FTIR spectra for CO₂ methanation over the Ni/ZrCe catalyst. Species identification: HC (hydrogen carbonate), MC (monodentate carbonate), BC (bidentate carbonate), PC (polydentate carbonate), F (formate), M (methoxy), FO (formaldehyde), and C (carboxylate).</p> Full article ">Figure 10
<p>Operando FTIR spectra for CO₂ methanation over the Ni/Ti catalyst. Species identification: HC (hydrogen carbonate), MC (monodentate carbonate), BC (bidentate carbonate), PC (polydentate carbonate), F (formate), M (methoxy), FO (formaldehyde), and C (carboxylate).</p> Full article ">Figure 11
<p>Scheme illustrating the formate pathway for CO₂ methanation on supported Ni catalysts.</p> Full article ">

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Supplementary material:
Supplementary File 1 (ZIP, 676 KiB)

13 pages, 5148 KiB  

Open AccessArticle

Carbon Fibers Prepared via Solution Plasma-Generated Seeds

by Andres Eduardo Romero Valenzuela, Chayanaphat Chokradjaroen, Pongpol Choeichom, Xiaoyang Wang, Kyusung Kim and Nagahiro Saito

Materials 2023, 16(3), 906; https://doi.org/10.3390/ma16030906 - 17 Jan 2023

Cited by 3 | Viewed by 2370

Abstract

Carbon fibers are materials with potential applications for CO₂ capture due to their porous structure and high surface areas. Nevertheless, controlling their porosity at a microscale remains challenging. The solution plasma (SP) process provides a fast synthesis route for carbon materials when [...] Read more.

Carbon fibers are materials with potential applications for CO₂ capture due to their porous structure and high surface areas. Nevertheless, controlling their porosity at a microscale remains challenging. The solution plasma (SP) process provides a fast synthesis route for carbon materials when organic precursors are used. During the discharge and formation of carbon materials in solution, a soot product-denominated solution plasma-generated seeds (SPGS) is simultaneously produced at room temperature and atmospheric pressure. Here, we propose a preparation method for carbon fibers with different and distinctive morphologies. The control over the morphology is also demonstrated by the use of different formulations. Full article

(This article belongs to the Topic Materials and Catalysts for Pollutants and CO₂ Capture and Transformation)

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Figure 1

Figure 1
<p>Concept for the utilization of SPGS for carbon fiber growth.</p> Full article ">Figure 2
<p>Experimental setup for the growth of carbon fibers using (a) benzene, (b) dichlorobenzene, (c) NMP, (d) ethanol and (e) methanol.</p> Full article ">Figure 3
<p>SEM micrographs of carbon fibers grown by (<b>a</b>,<b>b</b>) benzene, (<b>c</b>,<b>d</b>) dichlorobenzene, (<b>e</b>,<b>f</b>) NMP, (<b>g</b>,<b>h</b>) ethanol, and (<b>i</b>,<b>j</b>) methanol SPGS. Ni content at joints and tips is highlighted in yellow.</p> Full article ">Figure 4
<p>Crystalline structure of carbon fibers characterized by (<b>a</b>) XRD and (<b>b</b>) Raman spectroscopy.</p> Full article ">Figure 5
<p>Elemental composition of carbon fibers grown by (<b>a</b>) benzene, (<b>b</b>) dichlorobenzene, (<b>c</b>) NMP, (<b>d</b>) ethanol, and (<b>e</b>) methanol SPGS by energy-dispersive X-ray spectroscopy (EDX).</p> Full article ">Figure 6
<p>Nitrogen adsorption–desorption isotherms of carbon fibers grown by (<b>a</b>) benzene, (<b>b</b>) dichlorobenzene, (<b>c</b>) NMP, (<b>d</b>) ethanol, and (<b>e</b>) methanol SPGS at 77 K. (<b>f</b>) Pore volume and average pore size.</p> Full article ">Figure 7
<p>Precursor affecting the morphology of fibers.</p> Full article ">

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Supplementary material:
Supplementary File 1 (ZIP, 2829 KiB)

13 pages, 4021 KiB  

Open AccessArticle

Forced Mineral Carbonation of MgO Nanoparticles Synthesized by Aerosol Methods at Room Temperature

by Kyungil Cho, Yeryeong Kang, Sukbyung Chae and Changhyuk Kim

Nanomaterials 2023, 13(2), 281; https://doi.org/10.3390/nano13020281 - 9 Jan 2023

Cited by 1 | Viewed by 2009

Abstract

Magnesium oxide (MgO) has been investigated as a wet mineral carbonation adsorbent due to its relatively low adsorption and regeneration temperatures. The carbon dioxide (CO₂) capture efficiency can be enhanced by applying external force on the MgO slurry during wet carbonation. [...] Read more.

Magnesium oxide (MgO) has been investigated as a wet mineral carbonation adsorbent due to its relatively low adsorption and regeneration temperatures. The carbon dioxide (CO₂) capture efficiency can be enhanced by applying external force on the MgO slurry during wet carbonation. In this study, two aerosol-processed MgO nanoparticles were tested with a commercial MgO one to investigate the external force effect on the wet carbonation performance at room temperature. The MgO nano-adsorbents were carbonated and sampled every 2 h up to 12 h through forced and non-forced wet carbonations. Hydrated magnesium carbonates (nesquehonite, artinite and hydromagnesite) were formed with magnesite through both wet carbonations. The analyzed results for the time-dependent chemical compositions and physical shapes of the carbonation products consistently showed the enhancement of wet carbonation by the external force, which was at least 4 h faster than the non-forced carbonation. In addition, the CO₂ adsorption was enhanced by the forced carbonation, resulting in a higher amount of CO₂ being adsorbed by MgO nanoparticles than the non-forced carbonation, unless the carbonation processes were completed. The adsorbed amount of CO₂ was between the maximum theoretical amounts of CO₂ adsorbed by nesquehonite and hydromagnesite. Full article

(This article belongs to the Topic Materials and Catalysts for Pollutants and CO₂ Capture and Transformation)

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Figure 1

Figure 1
<p>XRD results of the samples for the non-forced (N) wet carbonations of (<b>a</b>) A-MgO, (<b>b</b>) C-MgO and (<b>c</b>) T-MgO as well as forced (F) wet carbonations of (<b>d</b>) A-MgO, (<b>e</b>) C-MgO and (<b>f</b>) T-MgO.</p> Full article ">Figure 2
<p>Morphological changes in the 3 MgO nano-adsorbents between pristine and 4 h carbonation products through the forced (F) or non-forced (N) wet carbonations for (<b>a</b>) A-MgO, (<b>b</b>) C-MgO and (<b>c</b>) T-MgO analyzed by FE-SEM (scale bars: 100 nm for pristine particles and 10 μm for carbonated samples) (SEM images at full carbonation time conditions are in the <a href="#app1-nanomaterials-13-00281" class="html-app">Supplementary Materials</a>) SI).</p> Full article ">Figure 3
<p>FT-IR spectra results of the pristine MgO nanoparticles and the products after non-forced wet carbonations of (<b>a</b>) A-MgO, (<b>b</b>) C-MgO and (<b>c</b>) T-MgO as well as forced wet carbonations of (<b>d</b>) A-MgO, (<b>e</b>) C-MgO and (<b>f</b>) T-MgO.</p> Full article ">Figure 4
<p>Adsorbed CO₂ masses per unit mass (M_CO2) of the forced (F) or non-forced (N) wet carbonation products analyzed by GC-TCD for (<b>a</b>) A-MgO, (<b>b</b>) C-MgO and (<b>c</b>) T-MgO. (<b>d</b>) M_CO2 of the F-carbonation products of the 3 MgO nano-adsorbents were compared with theoretical maximum CO₂ adsorption masses of the possible MgO carbonates such as magnesite, hydromagnesite, nesquehonite and artinite.</p> Full article ">Scheme 1
<p>Experimental setup for the forced or non-forced wet carbonations of 3 MgO nanoparticle adsorbents.</p> Full article ">

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Supplementary material:
Supplementary File 1 (ZIP, 11118 KiB)

22 pages, 11136 KiB  

Open AccessArticle

Low Overpotential Electrochemical Reduction of CO₂ to Ethanol Enabled by Cu/Cu_xO Nanoparticles Embedded in Nitrogen-Doped Carbon Cuboids

by Monther Q. Alkoshab, Eleni Thomou, Ismail Abdulazeez, Munzir H. Suliman, Konstantinos Spyrou, Wissam Iali, Khalid Alhooshani and Turki N. Baroud

Nanomaterials 2023, 13(2), 230; https://doi.org/10.3390/nano13020230 - 4 Jan 2023

Cited by 3 | Viewed by 2638

Abstract

The electrochemical conversion of CO₂ into value-added chemicals is a promising approach for addressing environmental and energy supply problems. In this study, electrochemical CO₂ catalysis to ethanol is achieved using incorporated Cu/Cu_xO nanoparticles into nitrogenous porous carbon cuboids. Pyrolysis [...] Read more.

The electrochemical conversion of CO₂ into value-added chemicals is a promising approach for addressing environmental and energy supply problems. In this study, electrochemical CO₂ catalysis to ethanol is achieved using incorporated Cu/Cu_xO nanoparticles into nitrogenous porous carbon cuboids. Pyrolysis of the coordinated Cu cations with nitrogen heterocycles allowed Cu nanoparticles to detach from the coordination complex but remain dispersed throughout the porous carbon cuboids. The heterogeneous composite Cu/Cu_xO-PCC-0h electrocatalyst reduced CO₂ to ethanol at low overpotential in 0.5 M KHCO₃, exhibiting maximum ethanol faradaic efficiency of 50% at −0.5 V vs. reversible hydrogen electrode. Such electrochemical performance can be ascribed to the synergy between pyridinic nitrogen species, Cu/Cu_xO nanoparticles, and porous carbon morphology, together providing efficient CO₂ diffusion, activation, and intermediates stabilization. This was supported by the notably high electrochemically active surface area, rich porosity, and efficient charge transfer properties. Full article

(This article belongs to the Topic Materials and Catalysts for Pollutants and CO₂ Capture and Transformation)

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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>(<b>a</b>,<b>b</b>) SEM images of the unleached PCC at different magnifications, (<b>c</b>) TEM image of two overlapping cuboids, (<b>d</b>) HRTEM demonstrating lattice fringe of a copper particle, (<b>e</b>) HRTEM image of one Cu nanoparticle.</p> Full article ">Figure 1 Cont.
<p>(<b>a</b>,<b>b</b>) SEM images of the unleached PCC at different magnifications, (<b>c</b>) TEM image of two overlapping cuboids, (<b>d</b>) HRTEM demonstrating lattice fringe of a copper particle, (<b>e</b>) HRTEM image of one Cu nanoparticle.</p> Full article ">Figure 2
<p>(<b>a</b>) HRTEM image of Cu/Cu_xO-PCC-0h (<b>b</b>) elemental mapping of the Cu/Cu_xO-PCC-0h (unleached PCC).</p> Full article ">Figure 3
<p>(<b>a</b>) XRD pattern, (<b>b</b>) XPS survey scan of Cu/Cu_xO-PCC-0h, (<b>c</b>) High-resolution XPS spectrum of N 1 s for Cu/Cu_xO-PCC-0h, (<b>d</b>) High-resolution XPS spectra of Cu 2p for Cu/Cu_xO-PCC-0h.</p> Full article ">Figure 3 Cont.
<p>(<b>a</b>) XRD pattern, (<b>b</b>) XPS survey scan of Cu/Cu_xO-PCC-0h, (<b>c</b>) High-resolution XPS spectrum of N 1 s for Cu/Cu_xO-PCC-0h, (<b>d</b>) High-resolution XPS spectra of Cu 2p for Cu/Cu_xO-PCC-0h.</p> Full article ">Figure 4
<p>High-resolution XPS spectra of Cu 2p for (<b>a</b>) Cu/Cu_xO-PCC-1h and (<b>b</b>) Cu/Cu_xO-PCC-6h.</p> Full article ">Figure 5
<p>(<b>a</b>) adsorption-desorption isotherm of the unleached PCC catalyst, Cu/Cu_xO-PCC-0h (<b>b</b>) adsorption-desorption isotherms of the leached PCC catalysts, Cu/Cu_xO-PCC-1h, Cu/Cu_xO-PCC-6h.</p> Full article ">Figure 6
<p>DFT pore size distribution for the three catalysts.</p> Full article ">Figure 7
<p>(<b>a</b>–<b>c</b>) LSV scans under Ar and CO₂ saturated electrolytes for Cu/Cu_xO-PCC-0h, Cu/Cu_xO-PCC-1h, and Cu/Cu_xO-PCC-6h, respectively.</p> Full article ">Figure 7 Cont.
<p>(<b>a</b>–<b>c</b>) LSV scans under Ar and CO₂ saturated electrolytes for Cu/Cu_xO-PCC-0h, Cu/Cu_xO-PCC-1h, and Cu/Cu_xO-PCC-6h, respectively.</p> Full article ">Figure 8
<p>(<b>a</b>–<b>c</b>) Faradaic efficiencies of different products against the potential for Cu/Cu_xO-PCC-0h, Cu/Cu_xO-PCC-1h, and Cu/Cu_xO-PCC-6h, respectively.</p> Full article ">Figure 9
<p>Schematic representation of the three catalysts.</p> Full article ">Figure 10
<p>(<b>a</b>–<b>c</b>) CV plots electrochemical double-layer measurement electrolytes for Cu/Cu_xO-PCC-0h, Cu/Cu_xO-PCC-1h, and Cu/Cu_xO-PCC-6h, respectively. (<b>d</b>) Electrochemical double layer plot (<b>e</b>) Nyquist plots at −0.5 V vs. RHE.</p> Full article ">Figure 10 Cont.
<p>(<b>a</b>–<b>c</b>) CV plots electrochemical double-layer measurement electrolytes for Cu/Cu_xO-PCC-0h, Cu/Cu_xO-PCC-1h, and Cu/Cu_xO-PCC-6h, respectively. (<b>d</b>) Electrochemical double layer plot (<b>e</b>) Nyquist plots at −0.5 V vs. RHE.</p> Full article ">Figure 11
<p>(<b>a</b>) Relative amounts of nitrogen species in the three samples, (<b>b</b>,<b>c</b>) Tafel plots of CO on Cu/Cu_xO-PCC-0h and Cu/Cu_xO-PCC-1h catalysts.</p> Full article ">

18 pages, 10307 KiB  

Open AccessReview

Research Progress in High-Throughput Screening of CO₂ Reduction Catalysts

by Qinglin Wu, Meidie Pan, Shikai Zhang, Dongpeng Sun, Yang Yang, Dong Chen, David A. Weitz and Xiang Gao

Energies 2022, 15(18), 6666; https://doi.org/10.3390/en15186666 - 13 Sep 2022

Cited by 15 | Viewed by 3729

Abstract

The conversion and utilization of carbon dioxide (CO₂) have dual significance for reducing carbon emissions and solving energy demand. Catalytic reduction of CO₂ is a promising way to convert and utilize CO₂. However, high-performance catalysts with excellent catalytic [...] Read more.

The conversion and utilization of carbon dioxide (CO₂) have dual significance for reducing carbon emissions and solving energy demand. Catalytic reduction of CO₂ is a promising way to convert and utilize CO₂. However, high-performance catalysts with excellent catalytic activity, selectivity and stability are currently lacking. High-throughput methods offer an effective way to screen high-performance CO₂ reduction catalysts. Here, recent advances in high-throughput screening of electrocatalysts for CO₂ reduction are reviewed. First, the mechanism of CO₂ reduction reaction by electrocatalysis and potential catalyst candidates are introduced. Second, high-throughput computational methods developed to accelerate catalyst screening are presented, such as density functional theory and machine learning. Then, high-throughput experimental methods are outlined, including experimental design, high-throughput synthesis, in situ characterization and high-throughput testing. Finally, future directions of high-throughput screening of CO₂ reduction electrocatalysts are outlooked. This review will be a valuable reference for future research on high-throughput screening of CO₂ electrocatalysts. Full article

(This article belongs to the Topic Materials and Catalysts for Pollutants and CO₂ Capture and Transformation)

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<p>Electrocatalytic system and principle of CO₂ electrocatalytic reaction. (<b>a</b>) Model of a typical electrocatalytic system. Reprinted with permission from Ref. [<a href="#B28-energies-15-06666" class="html-bibr">28</a>]. Copyright 2020, Elsevier. (<b>b</b>) Mechanism of CO₂ electrocatalytic reduction on electrodes in aqueous solutions. The formation paths of the five main C₁ products are illustrated during the reduction process. Reprinted with permission from Ref. [<a href="#B39-energies-15-06666" class="html-bibr">39</a>]. Copyright 2017, John Wiley and Sons. (<b>c</b>) C₂ and C₃ pathways starting from *CO on Cu surfaces. Reprinted with permission from Ref. [<a href="#B40-energies-15-06666" class="html-bibr">40</a>]. Copyright 2019, American Chemical Society.</p> Full article ">Figure 2
<p>Applications of machine learning in high-throughput screening of high-performance electrocatalysts for CO₂ reduction. (<b>a</b>) Steps of machine learning for high-throughput screening. Adapted with permission from Ref. [<a href="#B68-energies-15-06666" class="html-bibr">68</a>]. Copyright 2022, John Wiley and Sons. (<b>b</b>) Plots of CORR activity versus CO₂RR/CORR selectivity for CoCuGaNiZn systems (left) and AgAuCuPdPt systems (right) predicted by Gaussian process regression. Reprinted with permission from Ref. [<a href="#B72-energies-15-06666" class="html-bibr">72</a>]. Copyright 2020, American Chemical Society. CORR denotes CO reduction reaction. CO₂RR/CORR selectivity is defined as the probability of surface sites with weaker or the same H adsorption strength as Cu. CORR activity is defined as the ability to reduce CO further, as the joint independent probability of surface sites with weaker or the same H adsorption strength as Cu and stronger or the same CO adsorption strength as Cu. (<b>c</b>) ML-predicted and DFT-calculated free energies of different reaction pathways for CO₂RR to CO by Ag-MoPc (left) and Ag-CoPc (right). The * at the upper left of the substance name denotes that the substance is adsorbed on the surface of a catalyst. Reprinted with permission from Ref. [<a href="#B77-energies-15-06666" class="html-bibr">77</a>]. Copyright 2021, American Chemical Society.</p> Full article ">Figure 3
<p>General experimental steps involved in high-throughput screening of high-performance electrocatalysts for CO₂ reduction. Reprinted with permission from Ref. [<a href="#B57-energies-15-06666" class="html-bibr">57</a>]. Copyright 2022, John Wiley and Sons.</p> Full article ">Figure 4
<p>Experimental design for exploring the parameter space of catalysts. (<b>a</b>) Identification of the optimal active catalyst for hydrogen production by an ultrafast multidimensional group testing method. Reprinted with permission from Ref. [<a href="#B82-energies-15-06666" class="html-bibr">82</a>]. Copyright 2012, American Chemical Society. (<b>b</b>) A combinatorial strategy for identifying lead “hits” in catalyst discovery by deconvolution of complex catalyst mixtures. Reprinted with permission from Ref. [<a href="#B84-energies-15-06666" class="html-bibr">84</a>]. Copyright 2015, The Royal Society of Chemistry.</p> Full article ">Figure 5
<p>High-throughput synthesis of catalyst candidates. (<b>a</b>) Schematic diagram showing the preparation of catalysts by sputtering deposition. Reprinted with permission from Ref. [<a href="#B29-energies-15-06666" class="html-bibr">29</a>]. Copyright 2016, Elsevier. (<b>b</b>) Bright-field TEM image of the cross section of a thin multilayer film prepared by electron beam deposition. Reprinted with permission from Ref. [<a href="#B90-energies-15-06666" class="html-bibr">90</a>]. Copyright 2015, The Royal Society of Chemistry. (<b>c</b>) An automatic platform that can generate efficient pipetting-to-microplate workplans and support their reliable execution with visual guidance. Reprinted with permission from Ref. [<a href="#B92-energies-15-06666" class="html-bibr">92</a>]. Copyright 2022, American Chemical Society. (<b>d</b>) Operations performed autonomously in a combined liquid handling/capping station by mobile robots. Reprinted with permission from Ref. [<a href="#B93-energies-15-06666" class="html-bibr">93</a>]. Copyright 2020, Springer Nature. (<b>e</b>) Synthesis of multi-component mesoporous metal oxides using inkjet printing. Reprinted with permission from Ref. [<a href="#B82-energies-15-06666" class="html-bibr">82</a>]. Copyright 2012, American Chemical Society. (<b>f</b>) Controlled preparation of catalysts by flow chemistry in microfluidic channels. Reprinted with permission from Ref. [<a href="#B99-energies-15-06666" class="html-bibr">99</a>]. Copyright 2016, Elsevier.</p> Full article ">Figure 6
<p>Characterization and high-throughput testing of catalyst candidates. (<b>a</b>) In situ characterization methods for solid, interface and liquid catalysts. Reprinted with permission from Ref. [<a href="#B104-energies-15-06666" class="html-bibr">104</a>]. Copyright 2020, American Chemical Society. (<b>b</b>) Screening the performance of platinum catalysts by fluorescent intensity. Reprinted with permission from Ref. [<a href="#B80-energies-15-06666" class="html-bibr">80</a>]. Copyright 2021, Springer Nature. (<b>c</b>) Automatic, programmable sampling system for multichannel outputs. Reprinted with permission from Ref. [<a href="#B114-energies-15-06666" class="html-bibr">114</a>]. Copyright 2013, Elsevier. (<b>d</b>) In situ characterization of the electrochemical performance by mass spectrometry. Reprinted with permission from Ref. [<a href="#B29-energies-15-06666" class="html-bibr">29</a>]. Copyright 2016, Elsevier. (<b>e</b>) In situ characterization of the concentration of CO₂ and reaction products near the cathode surface by mass spectrometry. Reprinted with permission from Ref. [<a href="#B111-energies-15-06666" class="html-bibr">111</a>]. Copyright 2018, American Chemical Society. (<b>f</b>) Schematic diagram of an electrochemical flow cell with in situ product detection by mass spectrometry. Reprinted with permission from Ref. [<a href="#B115-energies-15-06666" class="html-bibr">115</a>]. Copyright 2019, American Chemical Society.</p> Full article ">

11 pages, 2255 KiB  

Open AccessArticle

Photo-Regeneration of Zeolite-Based Volatile Organic Compound Filters Enabled by TiO₂ Photocatalyst

by Taegyu Kim, Kunsang Yoo, Myung-Gil Kim and Yong-Hoon Kim

Nanomaterials 2022, 12(17), 2959; https://doi.org/10.3390/nano12172959 - 26 Aug 2022

Cited by 6 | Viewed by 2140

Abstract

Indoor air filtration received significant attention owing to the growing threat to the environment and human health caused by air pollutants such as volatile organic compound (VOC) gases. However, owing to the limited adsorption capacity of VOC adsorbents, such as activated carbon, a [...] Read more.

Indoor air filtration received significant attention owing to the growing threat to the environment and human health caused by air pollutants such as volatile organic compound (VOC) gases. However, owing to the limited adsorption capacity of VOC adsorbents, such as activated carbon, a rapid breakthrough can occur, reducing the service life of the filter. Therefore, TiO₂-coated zeolite (TiO₂/zeolite) was utilized as a photo-regenerative VOC adsorbent to increase the service life of VOC filters. In particular, with photoactive TiO₂ forms on zeolite, efficient and repetitive photo-regeneration is attainable through the dissociation of VOC molecules by the photocatalytic reaction. We optimized the TiO₂ coating amount to obtain TiO₂/zeolite particles with a high surface area (BET surface area > 500 m²/g) and high adsorption capacity. A VOC filter with an adsorption efficiency of 72.1% for formaldehyde was realized using TiO₂/zeolite as the adsorbent. Furthermore, the TiO₂/zeolite filter exhibits a photo-regeneration efficiency of >90% for the initial two regeneration cycles using ultraviolet illumination, and >60% up to five cycles. Based on these observations, we consider that TiO₂/zeolite is a potential adsorbent candidate for photo-regenerative VOC filters. Full article

(This article belongs to the Topic Materials and Catalysts for Pollutants and CO₂ Capture and Transformation)

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<p>(<b>a</b>) Fabrication process and schematic photo-regeneration process of TiO₂/zeolite-based VOC filters. FESEM images of TiO₂/zeolite particles fabricated with different T:Z ratios, (<b>b</b>) T:Z = 0.5:1, (<b>c</b>) 1:1, (<b>d</b>) 1.5:1, and (<b>e</b>) 2:1. Corresponding EDS elemental mapping images (Ti Ka1) of TiO₂/zeolite particles fabricated with different T:Z ratios, (<b>f</b>) T:Z = 0.5:1, (<b>g</b>) 1:1, (<b>h</b>) 1.5:1, and (<b>i</b>) 2:1. The scale bars in the images indicate 2 μm.</p> Full article ">Figure 2
<p>(<b>a</b>) Variation in atomic composition of zeolite and TiO₂/zeolite particle surfaces synthesized with different T:Z ratios (elements: O, Na, Al, Si, and Ti). T:Z ratio of 0:1 indicates bare zeolite particles. Variations in (<b>b</b>) BET surface area, (<b>c</b>) average pore size, and (<b>d</b>) total pore volume of TiO₂/zeolite particles as a function of T:Z ratio.</p> Full article ">Figure 3
<p>BET nitrogen adsorption and desorption isotherm data of zeolite and TiO₂/zeolite particles fabricated with different T:Z ratios, (<b>a</b>) T:Z = 0:1, (<b>b</b>) 0.5:1, (<b>c</b>) 1:1, (<b>d</b>) 1.5:1, and (<b>e</b>) 2:1.</p> Full article ">Figure 4
<p>(<b>a</b>) Optical images of TiO₂/zeolite VOC filter fabricated using the spray-coating method. (<b>b</b>) FESEM images of TiO₂/zeolite particles coated on the VOC filter.</p> Full article ">Figure 5
<p>(<b>a</b>) Variation in formaldehyde concentration for bare zeolite and TiO₂/zeolite VOC filters as a function of filtering time. (<b>b</b>) Relative formaldehyde concentration (C/C₀) changes as a function of filtering time. Here, C₀ and C indicate formaldehyde concentration before and during the filtering process, respectively. (<b>c</b>) The variation in formaldehyde concentration and (<b>d</b>) C/C₀ as a function of filtering time after the first regeneration process. (<b>e</b>) Relative formaldehyde concentration (C/C₀) change for five regeneration processes (TiO₂/zeolite filter). (<b>f</b>) Variation in regeneration efficiency as a function of regeneration number.</p> Full article ">Figure 6
<p>(<b>a</b>) Variation in toluene concentration for bare zeolite and TiO₂/zeolite VOC filters as a function of filtering time. (<b>b</b>) Relative toluene concentration (C/C₀) changes as a function of filtering time. Here, C₀ and C indicate toluene concentration before and during the filtering process, respectively. (<b>c</b>) Variation in toluene concentration and (<b>d</b>) C/C₀ as a function of filtering time after the first regeneration process. (<b>e</b>) Relative toluene concentration (C/C₀) change for five regeneration processes (TiO₂/zeolite filter). (<b>f</b>) Variation in regeneration efficiency as a function of regeneration number.</p> Full article ">

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Supplementary material:
Supplementary File 1 (ZIP, 1506 KiB)

11 pages, 3183 KiB  

Open AccessArticle

Formic Acid Generation from CO₂ Reduction by MOF-253 Coordinated Transition Metal Complexes: A Computational Chemistry Perspective

by Meng-Chi Hsieh, Ranganathan Krishnan and Ming-Kang Tsai

Catalysts 2022, 12(8), 890; https://doi.org/10.3390/catal12080890 - 12 Aug 2022

Cited by 4 | Viewed by 2968

Abstract

The inclusion of transition metal elements within metal–organic frameworks (MOFs) is considered one of the most promising approaches for enhancing the catalytic capability of MOFs. In this study, MOF-253 containing bipyridine coordination sites is investigated for possible transition metal chelation, and a consequent [...] Read more.

The inclusion of transition metal elements within metal–organic frameworks (MOFs) is considered one of the most promising approaches for enhancing the catalytic capability of MOFs. In this study, MOF-253 containing bipyridine coordination sites is investigated for possible transition metal chelation, and a consequent possible CO₂ reduction mechanism in the formation of formic acid. All transition metal elements of the third, fourth and fifth periods except hafnium and the lanthanide series are considered using density functional theory calculations. Two distinct types of CO₂ reduction mechanisms are identified: (1) the five-coordination Pd center, which promotes formic acid generation via an intramolecular proton transfer pathway; (2) several four-coordination metal centers, including Mn, Pd, and Pt, which generate formic acid by means of heterolytic hydrogen activation. The MOF-253 environment is found to promote beneficial steric hindrance, and to constrain metal–ligand orientation, which consequently facilitates the formation of formic acid, particularly with the tetrahedral Mn center at high-spin electronic state. Full article

(This article belongs to the Topic Materials and Catalysts for Pollutants and CO₂ Capture and Transformation)

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<p>Proposed reaction pathways of CO₂ reduction by LMCl₂ complexes. The gray pathways are unfavorable cases; green and blue pathways are accessible cases.</p> Full article ">Figure 2
<p>(<b>a</b>) The H₂ adsorption energies and bond lengths of LMCl₂(H₂) intermediates where basis set superposition errors are corrected; LS, MS, and HS denote the low-spin, high-spin, and medium spin states of complexes, respectively (see <a href="#app1-catalysts-12-00890" class="html-app">Table S3</a>); (<b>b</b>) The CO₂ desorption energies of low-spin LMCl₂(CO₂) intermediates.</p> Full article ">Figure 3
<p>The predicted catalytic mechanism of HCOOH(g) generation by the (bpydc)PdCl(H)₂ complex with H₂(g) + CO₂(g).</p> Full article ">Figure 4
<p>The predicted catalytic mechanism of formic acid generation by high-spin (s = 5/2) (bpydc)MnCl(H) complex with H₂(g) + CO₂(g). [TS*] denotes the approximate transition state.</p> Full article ">Figure 5
<p>The predicted catalytic mechanism of formic acid generation by singlet (bpydc)MCl(H), M = Pd or Pt complex with H₂(g) + CO₂(g). The solid black and dashed red lines denote the catalytic pathways conducted by Pd and Pt complexes, respectively, and share the same text labels as the predicted intermediates. [TS*] denotes the approximate transition state.</p> Full article ">Figure 6
<p>The predicted catalytic mechanism (blue lines) of formic acid generation by L_mofMnCl(H) catalytic site with H₂(g) + CO₂(g). The gray lines denote the mechanism of the molecular model. [TS*] denotes the approximate transition state.</p> Full article ">Figure 7
<p>Schematic comparisons of LMnCl(HCO₂), HLMnCl(HCOOH), and HLMnCl(CO₂) intermediates using the molecular (<b>a</b>–<b>c</b>) and periodic (<b>d</b>–<b>f</b>) models, respectively.</p> Full article ">

10 pages, 5949 KiB  

Open AccessArticle

Efficient Photothermal Elimination of Formaldehyde under Visible Light at Room Temperature by a MnO_x-Modified Multi-Porous Carbon Sphere

by Wanpeng Liu, Liu Shi, Rongyang Yin, Pengfei Sun, Jinming Ren and Yongming Wang

Materials 2022, 15(13), 4484; https://doi.org/10.3390/ma15134484 - 25 Jun 2022

Cited by 7 | Viewed by 1875

Abstract

Volatile organic compounds (VOCs) exert a serious impact on the environment and human health. The development of new technologies for the elimination of VOCs, especially those from non-industrial emission sources, such as indoor air pollution and other low-concentration VOCs exhaust gases, is essential [...] Read more.

Volatile organic compounds (VOCs) exert a serious impact on the environment and human health. The development of new technologies for the elimination of VOCs, especially those from non-industrial emission sources, such as indoor air pollution and other low-concentration VOCs exhaust gases, is essential for improving environmental quality and human health. In this study, a monolithic photothermocatalyst was prepared by stabilizing manganese oxide on multi-porous carbon spheres to facilitate the elimination of formaldehyde (HCHO). This catalyst exhibited excellent photothermal synergistic performance. Therefore, by harvesting only visible light, the catalyst could spontaneously heat up its surface to achieve a thermal catalytic oxidation state suitable for eliminating HCHO. We found that the surface temperature of the catalyst could reach to up 93.8 °C under visible light, achieving an 87.5% HCHO removal efficiency when the initial concentration of HCHO was 160 ppm. The microporous structure on the surface of the carbon spheres not only increased the specific surface area and loading capacity of manganese oxide but also increased their photothermal efficiency, allowing them to reach a temperature high enough for MnO_x to overcome the activation energy required for HCHO oxidation. The relevant catalyst characteristics were analyzed using XRD, measurement of BET surface area, scanning electron microscopy, HR-TEM, XPS, and DRS. Results obtained from a cyclic performance test indicated high stability and potential application of the MnO_x-modified multi-porous carbon sphere. Full article

(This article belongs to the Topic Materials and Catalysts for Pollutants and CO₂ Capture and Transformation)

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<p>The HCHO elimination rate under xenon light irradiation by Mn-modified CNS catalysts with different synthesis conditions: (<b>A</b>) 0.005, 0.01, and 0.05 mol/L of potassium permanganate impregnated for 5 min; (<b>B</b>) 0.005, 0.01, and 0.05 mol/L of potassium permanganate impregnated for 10 min; and (<b>C</b>) 0.005, 0.01, and 0.05 mol/L of potassium permanganate impregnated for 30 min.</p> Full article ">Figure 2
<p>(<b>A</b>) The HCHO elimination rate under xenon light irradiation by Mn-PCNS catalysts under processing temperatures. (<b>B</b>) The HCHO elimination rate under xenon light irradiation by 0.05MnC-30, PCNS-500, 0.05MnC-30-500, and 0.05MnC-60-500 catalysts.</p> Full article ">Figure 3
<p>N₂ adsorption (full symbols)–desorption (empty symbols) isotherms of PCNS-400, PCNS-500, and PCNS-600.</p> Full article ">Figure 4
<p>(<b>A</b>) Catalytic performance of PCNS and Mn-PCNS for HCHO elimination with and without irradiation. (<b>B</b>) Catalytic performance of CNS and Mn-CNS for HCHO elimination with and without irradiation; (<b>C</b>)UV-Vis-NIR DRS profiles of CNS, 0.05MnC-30, PCNS-500, and 0.05MnC-30-500. (<b>D</b>) Change in surface temperature of catalysts under visible light irradiation.</p> Full article ">Figure 5
<p>(<b>A</b>) XRD profiles of CNS, Zn-CNS, and PCNS-500; (<b>B</b>) XRD profiles of 0.05MnC-30-500 and PCNS-500.</p> Full article ">Figure 6
<p>SEM images of PCNS-500 (<b>A</b>–<b>C</b>), SEM images of Mn modified PCNS-5000 with 0.05 mol/L of potassium permanganate impregnated for 30 min (<b>D</b>–<b>F</b>), EDX-mapping test of element Mn, C, and O of Mn modified PCNS-500 ((<b>G</b>–<b>I</b>) related to SEM image of (<b>E</b>)).</p> Full article ">Figure 7
<p>HR-TEM profile of sample 0.05MnC-30-500.</p> Full article ">Figure 8
<p>XPS spectrum of 0.05Mn-C-30-500 and 0.05MnC-30: (<b>A</b>) Mn2p; (<b>B</b>) O1s: (<b>C</b>) C1s.</p> Full article ">Figure 9
<p>Cyclic performance test of 0.05MnC-30-500 for HCHO removal.</p> Full article ">

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Supplementary material:
Supplementary File 1 (ZIP, 611 KiB)

17 pages, 33373 KiB  

Open AccessArticle

Mechanistic and Experimental Study of the Cu_xO@C Nanocomposite Derived from Cu₃(BTC)₂ for SO₂ Removal

by Rudi Duan, Weibin Chen, Ziwei Chen, Jialiang Gu, Zhaoqi Dong, Beini He, Lili Liu and Xidong Wang

Catalysts 2022, 12(7), 689; https://doi.org/10.3390/catal12070689 - 24 Jun 2022

Viewed by 2266

Abstract

A tunable and efficient strategy was adopted to synthesize highly porous nano-structured CuO−carbonized composites (Cu_xO@C) using Cu₃(BTC)₂ as a sacrificial template. The as-synthesized CuO nanocomposites exhibited hollow octahedral structures, a large surface area (89.837 m² g⁻¹ [...] Read more.

A tunable and efficient strategy was adopted to synthesize highly porous nano-structured CuO−carbonized composites (Cu_xO@C) using Cu₃(BTC)₂ as a sacrificial template. The as-synthesized CuO nanocomposites exhibited hollow octahedral structures, a large surface area (89.837 m² g⁻¹) and a high proportion of Cu₂O active sites distributed on a carbon frame. Based on DFT calculations, both the Cu atoms on the surface (Cu_S) and oxygen vacancy (O_V) exhibited strong chemical reactivity. On the perfect CuO (111), the Cu_S transferred charge to O atoms on the surface and SO₂ molecules. A strong adsorption energy (−1.41 eV) indicated the existence of the chemisorption process. On the oxygen-deficient CuO (111), the O₂ preferably adsorbed on O_V and then formed SO₃ by bonding with SO₂, followed by the cleavage of the O−O bond. Furthermore, the CuO nanocomposites exhibited an excellent ratio of S/Cu in SO₂ removal experiments compared with CuO nanoparticles produced by coprecipitation. Full article

(This article belongs to the Topic Materials and Catalysts for Pollutants and CO₂ Capture and Transformation)

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<p>The morphology and phase of nano−CuOs. TEM images of (<b>a</b>,<b>b</b>) CuO−NC and (<b>d</b>,<b>e</b>) CuO−NP. The inset of (<b>a</b>) is the corresponding magnified image; STEM image (<b>c</b>) and elemental mapping images (<b>c1</b>–<b>c3</b>) of CuO−NC; XRD patterns of (<b>f</b>) Nano−CuOs and (inset) Cu₃(BTC)₂; and (<b>g</b>) TGA and DTA curves of Cu₂(BTC)₃.</p> Full article ">Figure 2
<p>Porosity analysis of nano−CuOs. (<b>a</b>) N₂ isotherms of adsorption-desorption curves at 77 K and their corresponding and (<b>b</b>) pore size distributions. The inset of (<b>a</b>,<b>b</b>) is the correspondingly enlarged view of CuO−NP.</p> Full article ">Figure 3
<p>Chemical compositions of nano−CuOs. (<b>a</b>) Cu 2p XPS spectra, (<b>b</b>) O 1s XPS spectra, (<b>c</b>) Raman spectra and (<b>d</b>) EPR spectra of CuO−NC and CuO−NP. The inset of (<b>d</b>) is the correspondingly enlarged view of CuO−NP.</p> Full article ">Figure 4
<p>Adsorption configurations of SO₂ molecules over simulated CuO−NC (111). (Cu, O and S atoms are depicted in blue, red and yellow, respectively). (<b>a</b>) The unit cell of CuO (111). (<b>b</b>) The front view. (<b>c</b>) The adsorption configurations of the SO₂−adorbed intermediate. (<b>d</b>) The side view. (<b>e</b>) The CDD diagrams of the SO₂ adsorption over CuO surface. (<b>f</b>,<b>g</b>) The corresponding side and front views, respectively. (The yellow and the turquoise region refer to the charge consumption and accumulation, respectively). (<b>h</b>) The 2D sectional view of CDD diagrams.</p> Full article ">Figure 5
<p>The DOS for SO₂ molecules (<b>a</b>,<b>b</b>) and Cu atom (<b>c</b>) before and after adsorption, where the Cu atom is Cu on the surface of CuO. The Fermi energy corresponds to zero.</p> Full article ">Figure 6
<p>Adsorption configuration of SO₂ molecules on the oxygen-vacancy CuO (111) (Cu, O and S atoms are depicted in blue, red and yellow, respectively). (<b>a</b>)The oxygen vacancy on CuO (111). (<b>b</b>) O₂ adsorption on CuO (111) surface. (<b>c</b>) Optimized configurations of SO₂ adsorption on O₂−adsorbed CuO (111). (<b>d</b>) SO₂ adsorption on CuO (111).</p> Full article ">Figure 7
<p>FGD test results of nano−CuOs. (<b>a</b>) Adsorption isotherms of SO₂ in CuO−NC and CuO−NP at different temperatures. (<b>b</b>) The influence of reaction temperature on the SO₂ removal performance of CuO−NC and CuO−NP. (The Efficiency threshold was defined as 50%) (<b>c</b>) The influence of reaction atmosphere on the SO₂ removal performance of CuO−NC. (GHSV = 8900 h⁻¹, C_SO₂ = 2000 ppm).</p> Full article ">Figure 8
<p>Schematic of the synthesis process of nano−CuOs.</p> Full article ">

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Supplementary material:
Supplementary File 1 (ZIP, 1196 KiB)

18 pages, 11057 KiB  

Open AccessArticle

One-Pot Synthesis of Rubber Seed Shell-Derived N-Doped Ultramicroporous Carbons for Efficient CO₂ Adsorption

by Xiaoxia Zhang, Meng Rong, Hui Cao and Tianwei Tan

Nanomaterials 2022, 12(11), 1889; https://doi.org/10.3390/nano12111889 - 31 May 2022

Cited by 5 | Viewed by 2339

Abstract

In this work, a series of novel rubber seed shell-derived N-doped ultramicroporous carbons (NPCs) were prepared by one-step high-temperature activation (500–1000 °C), using melamine as the nitrogen source and KOH as the activator. The effects of the melamine dosage and the activation temperatures [...] Read more.

In this work, a series of novel rubber seed shell-derived N-doped ultramicroporous carbons (NPCs) were prepared by one-step high-temperature activation (500–1000 °C), using melamine as the nitrogen source and KOH as the activator. The effects of the melamine dosage and the activation temperatures on the surface chemical properties (doped N contents and N species), textural properties (surface area, pore structure, and microporosity), CO₂ adsorption capacities, and CO₂/N₂ selectivity were thoroughly investigated and characterized. These as-prepared NPCs demonstrate controllable BET surface areas (398–2163 m²/g), ultramicroporosity, and doped nitrogen contents (0.82–7.52 wt%). It was found that the ultramicroporosity and the doped nitrogens significantly affected the CO₂ adsorption and the separation performance at low pressure. Among the NPCs, highly microporous NPC-600-4 demonstrates the largest CO₂ adsorption capacity of 5.81 mmol/g (273 K, 1.0 bar) and 3.82 mmol/g (298 K, 1.0 bar), as well as a high CO₂/N₂ selectivity of 36.6, surpassing a lot of reported biomass-based porous carbons. In addition, NPC-600-4 also shows excellent thermal stability and recycle performance, indicating the competitive application potential in practical CO₂ capture. This work also presents a facile one-pot synthesis method to prepare high-performance biomass-based NPCs. Full article

(This article belongs to the Topic Materials and Catalysts for Pollutants and CO₂ Capture and Transformation)

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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>FT-IR spectra of NPC-700-x (<b>a</b>) and NPC-y-4 (<b>b</b>).</p> Full article ">Figure 2
<p>XPS (<b>a</b>), N1s XPS (<b>b</b>–<b>e</b>) spectra of NPC-y-4, and the contents of the nitrogen group in NPC-y-4 (<b>f</b>).</p> Full article ">Figure 3
<p>C1s XPS spectra of NPC-500-4 (<b>a</b>), NPC-600-4 (<b>b</b>), NPC-700-4 (<b>c</b>), NPC-800-4 (<b>d</b>), NPC-900-4 (<b>e</b>) and NPC-500-4 (<b>f</b>).</p> Full article ">Figure 4
<p>SEM images of NPC-700-x (<b>a</b>–<b>e</b>) and NPC-y-4 (<b>f</b>–<b>j</b>).</p> Full article ">Figure 5
<p>X-ray diffraction patterns of NPC-700-x (<b>a</b>) and NPC-y-4 (<b>b</b>).</p> Full article ">Figure 6
<p>Raman spectra of NPC-y-4.</p> Full article ">Figure 7
<p>77 K N₂ adsorption (filled) and desorption (empty) isotherms (<b>a</b>,<b>c</b>) and pore size distributions (<b>b</b>,<b>d</b>) of NPC-700-x and NPC-y-4.</p> Full article ">Figure 8
<p>CO₂ adsorption–desorption isotherms at 273 K and 298 K for NPC-700-x (<b>a</b>,<b>b</b>) and NPC-y-4 (<b>c</b>,<b>d</b>).</p> Full article ">Figure 9
<p>Isosteric heat of CO₂ adsorption as a function of CO₂ uptake for NPC-700-x (<b>a</b>) and NPC-y-4 (<b>b</b>).</p> Full article ">Figure 10
<p>CO₂ and N₂ adsorption isotherms of NPC-y-4 (<b>a</b>–<b>f</b>) at 298 K.</p> Full article ">Figure 11
<p>IAST CO₂/N₂ adsorption selectivity of NPC-700-x (<b>a</b>) and NPC-y-4 (<b>b</b>) at 298 K.</p> Full article ">Figure 12
<p>Five consecutive adsorption–desorption cycles of NPC-600-4 at 273 K.</p> Full article ">Scheme 1
<p>Synthetic illustration of the synthesis of RSS-based NPCs.</p> Full article ">

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Supplementary material:
Supplementary File 1 (ZIP, 1138 KiB)

14 pages, 14544 KiB  

Open AccessArticle

Silver Nanoparticle-Intercalated Cotton Fiber for Catalytic Degradation of Aqueous Organic Dyes for Water Pollution Mitigation

by Matthew Blake Hillyer, Jacobs H. Jordan, Sunghyun Nam, Michael W. Easson and Brian D. Condon

Nanomaterials 2022, 12(10), 1621; https://doi.org/10.3390/nano12101621 - 10 May 2022

Cited by 10 | Viewed by 2645

Abstract

Azo dyes are commonly used in textile color processing for their wide array of vibrant colors. However, in recent years these dyes have become of concern in wastewater management given their toxicity to humans and the environment. In the present work, researchers remediated [...] Read more.

Azo dyes are commonly used in textile color processing for their wide array of vibrant colors. However, in recent years these dyes have become of concern in wastewater management given their toxicity to humans and the environment. In the present work, researchers remediated water contaminated with azo dyes using silver nanoparticles (Ag NPs) intercalated within cotton fabric as a catalyst, for their enhanced durability and reusability, in a reductive degradation method. Three azo dyes—methyl orange (MO), Congo red (CR), and Chicago Sky Blue 6B (CSBB)—were investigated. The azo degradation was monitored by UV/vis spectroscopy, degradation capacity, and turnover frequency (TOF). The Ag NP–cotton catalyst exhibited excellent degradation capacity for the dyes, i.e., MO (96.4% in 30 min), CR (96.5% in 18.5 min), and CSBB (99.8% in 21 min), with TOFs of 0.046 min⁻¹, 0.082 min⁻¹, and 0.056 min⁻¹, respectively, using a 400 mg loading of catalyst for 100 mL of 25 mg L⁻¹ dye. To keep their high reusability while maintaining high catalytic efficiency of >95% degradation after 10 cycles, Ag NPs immobilized within cotton fabric have promising potential as eco-friendly bio-embedded catalysts. Full article

(This article belongs to the Topic Materials and Catalysts for Pollutants and CO₂ Capture and Transformation)

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Figure 1

Figure 1
<p>(<b>a</b>) UV/vis spectra of pristine white cotton (solid black line), synthesized Ag NP–cotton catalyst (solid yellow line) with maximum absorption at 420 nm, and Ag NP–cotton catalyst after 10 degradation cycles (dotted black line). Digital microscope images at 50× magnification of (<b>b</b>) pristine white cotton fabric and (<b>c</b>) Ag NP–cotton catalyst fabric.</p> Full article ">Figure 2
<p>(<b>a</b>,<b>b</b>) Histogram and cumulative percentage of Ag NP size distribution (9.7 ± 3.2 nm) in the Ag NP–cotton catalyst as determined by (<b>c</b>) TEM image of the Ag NP–cotton catalyst fiber cross-section, confirming the internal formation and uniform distribution of Ag NPs within the entirety of the fiber.</p> Full article ">Figure 3
<p>(<b>a</b>–<b>c</b>) UV/vis spectra of decreasing dye concentrations (λ_max denoted by the vertical dotted line) and (<b>d</b>–<b>f</b>) corresponding calibration curves with equations and linear regressions inset for methyl orange, Congo red, and Chicago Sky Blue 6B, respectively.</p> Full article ">Figure 4
<p>(<b>a</b>–<b>c</b>) UV/vis spectra for percentage dye concentration remaining, and (<b>d</b>–<b>f</b>) time plots of percent dye degradation for the catalytic reduction of MO, CR, and CSBB, respectively, by NaBH₄ in the presence of 200 mg Ag NP–cotton.</p> Full article ">Figure 5
<p>(<b>a</b>–<b>c</b>) UV/vis spectra of percentage dye concentration remaining, and (<b>d</b>–<b>f</b>) time plots of percentage dye degradation for the catalytic reduction of MO, CR, and CSBB, respectively, by NaBH₄ in the presence of 400 mg Ag NP–cotton.</p> Full article ">Figure 6
<p>(<b>a</b>–<b>c</b>) UV/vis spectra of percentage dye concentration remaining, and (<b>d</b>–<b>f</b>) time plots of percentage dye degradation for the catalytic reduction of MO, CR, and CSBB, respectively, by NaBH₄ in the presence of 200 mg Ag NP–cotton at pH 9.</p> Full article ">Figure 7
<p>Catalytic activity of Ag NP–cotton catalyst against consecutive degradation reaction cycles.</p> Full article ">Scheme 1
<p>Plausible mechanism for the Ag-catalytic reduction of azo-dyes by NaBH₄, where R and R’ represent carbon-based functional groups, and H-A represents water as a proton source.</p> Full article ">

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Supplementary material:
Supplementary File 1 (ZIP, 996 KiB)

16 pages, 4520 KiB  

Open AccessArticle

Silica-Supported Copper (II) Oxide Cluster via Ball Milling Method for Catalytic Combustion of Ethyl Acetate

by Yuhang Ye, Han Chen, Yuchuan Ye, Huiqiu Zhang, Jing Xu, Luhui Wang and Liuye Mo

Catalysts 2022, 12(5), 497; https://doi.org/10.3390/catal12050497 - 29 Apr 2022

Cited by 6 | Viewed by 2985

Abstract

Highly dispersed CuO/SiO₂ catalysts were successfully synthesized by a green process of ball milling (BM) under solvent-free and room temperature conditions. The structural evolution of CuO/SiO₂ catalysts prepared by BM was elucidated by TG-DSC, XRD, FT-IR, and XPS characterizations. We found [...] Read more.

Highly dispersed CuO/SiO₂ catalysts were successfully synthesized by a green process of ball milling (BM) under solvent-free and room temperature conditions. The structural evolution of CuO/SiO₂ catalysts prepared by BM was elucidated by TG-DSC, XRD, FT-IR, and XPS characterizations. We found that the copper acetate precursor was dispersed over the layer of copper phyllosilicate which was formed by reacting between the copper acetate precursor and the silica support during the BM process. The copper phyllosilicate layer over the support might play an important role in the stabilization of the CuO cluster (<2 nm) during thermal pretreatment. The 15% CuO/SiO₂ catalyst exhibited the best catalytic activity for the catalytic combustion of ethyl acetate as it owned a highest active surface area of CuO among the CuO/SiO₂ catalysts with different copper loadings. Full article

(This article belongs to the Topic Materials and Catalysts for Pollutants and CO₂ Capture and Transformation)

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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>TG/DSC curves of Cu (OAC)₂·H₂O (<b>a</b>) and 20%Cu-A-BM (<b>b</b>).</p> Full article ">Figure 2
<p>XRD patterns of W%Cu-A-BM, 10%Cu-O-BM, 10%Cu-N-IM catalysts calcined at 500 °C.</p> Full article ">Figure 3
<p>XRD patterns of 20%Cu-A-BM samples pretreated at different temperatures.</p> Full article ">Figure 4
<p>FT-IR spectra of 20% Cu-A-BM samples calcined at different temperatures.</p> Full article ">Figure 5
<p>Cu2p spectra of CuO/SiO₂ catalysts.</p> Full article ">Figure 6
<p>TPR profiles of CuO/SiO₂ catalysts prepared from different precursors and methods.</p> Full article ">Figure 7
<p>TPR profiles of W% Cu-A-BM catalysts.</p> Full article ">Figure 8
<p>HAADF-STEM and particle size statistics of 15% Cu-A-BM catalyst.</p> Full article ">Figure 9
<p>Catalytic activity of 10% Cu-A-BM, 10% Cu-O-BM, 10% Cu-N-IM (<b>a</b>) and W% Cu-A-BM catalysts (<b>b</b>).</p> Full article ">Figure 10
<p>Effect of copper loading over the W% Cu-A-BM catalysts on the copper active surfaces and the T₉₀.</p> Full article ">Scheme 1
<p>Simplified diagrammatic evolution of W% Cu-A-BM catalysts.</p> Full article ">

13 pages, 3028 KiB  

Open AccessArticle

Oxide Derived Copper for Electrochemical Reduction of CO₂ to C₂₊ Products

by Anum Zahid, Afzal Shah and Iltaf Shah

Nanomaterials 2022, 12(8), 1380; https://doi.org/10.3390/nano12081380 - 18 Apr 2022

Cited by 25 | Viewed by 4107

Abstract

The electrochemical reduction of carbon dioxide (CO₂) on copper electrode derived from cupric oxide (CuO), named oxide derived copper (ODCu), was studied thoroughly in the potential range of −1.0 V to −1.5 V versus RHE. The CuO nanoparticles were prepared by [...] Read more.

The electrochemical reduction of carbon dioxide (CO₂) on copper electrode derived from cupric oxide (CuO), named oxide derived copper (ODCu), was studied thoroughly in the potential range of −1.0 V to −1.5 V versus RHE. The CuO nanoparticles were prepared by the hydrothermal method. The ODCu electrode was used for carbon dioxide reduction and the results revealed that this electrode is highly selective for C₂₊ products with enhanced current density at significantly less overpotential. This catalyst shifts the selectivity towards C₂₊ products with the highest Faradaic efficiency up to 58% at −0.95 V. In addition, C₂ product formation at the lowest onset potential of −0.1 V is achieved with the proposed catalyst. X-ray diffraction and scanning electron microscopy revealed the reduction of CuO to Cu (111) nanoparticles during the CO₂ RR. The intrinsic property of the synthesized catalyst and its surface reduction are suggested to induce sites or edges for facilitating the dimerization and coupling of intermediates to ethanol and ethylene. Full article

(This article belongs to the Topic Materials and Catalysts for Pollutants and CO₂ Capture and Transformation)

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Figure 1

Figure 1
<p>SEM image of CuO (<b>a</b>) before and (<b>b</b>) after electrochemical reduction at −0.95 V vs. RHE.</p> Full article ">Figure 2
<p>The X-ray diffraction pattern of CuO before and after electrochemical reduction at −0.95 V vs. RHE.</p> Full article ">Figure 3
<p>Cyclic voltammetry measurements under N₂ and CO₂ atmosphere using CuO catalyst. Scan rate: 100 mV s⁻¹.</p> Full article ">Figure 4
<p>EIS spectra of catalyst in 5 mM K₃Fe(CN)₆ solution. Frequency range is from 1 Hz to 14 kHz.</p> Full article ">Figure 5
<p>Reduction current density of CO₂ as a function of time. Electrolyte: 0.5 M KHCO₃.</p> Full article ">Figure 6
<p>(<b>A</b>) CO₂ reduction Faradic efficiency as a function of potential; (<b>B</b>) Plot of log J vs. potential Faradaic efficiencies of C₂₊ (ethene, ethanol and propanol) on Cu Nano catalyst in the current density range of 10–70 mA/cm². Electrolyte: 0.5 M KHCO₃; (<b>C</b>) Chronoamperometry results at −0.8 V.</p> Full article ">Figure 7
<p>(<b>A</b>) Tafel plot for ethanol (<b>B</b>) Tafel plot for ethylene.</p> Full article ">Figure 8
<p>Proposed mechanism for the electroreduction of CO₂ to ethylene and ethanol on copper surfaces.</p> Full article ">

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Supplementary material:
Supplementary File 1 (ZIP, 270 KiB)

15 pages, 3567 KiB  

Open AccessArticle

Efficient Adsorption-Assisted Photocatalysis Degradation of Congo Red through Loading ZIF-8 on KI-Doped TiO₂

by Zhechen Liu, Wanqi Zhang, Xilong Zhao, Xianliang Sheng, Zichu Hu, Qiang Wang, Zhangjing Chen, Sunguo Wang, Xiaotao Zhang and Ximing Wang

Materials 2022, 15(8), 2857; https://doi.org/10.3390/ma15082857 - 13 Apr 2022

Cited by 9 | Viewed by 2675

Abstract

Zeolitic imidazolate framework-8 (ZIF-8) was evenly loaded on the surface of TiO₂ doped with KI, using a solvent synthesis method, in order to produce a ZIF-8@TiO₂ (KI) adsorption photocatalyst with good adsorption and photocatalytic properties. The samples were characterized by XRD, [...] Read more.

Zeolitic imidazolate framework-8 (ZIF-8) was evenly loaded on the surface of TiO₂ doped with KI, using a solvent synthesis method, in order to produce a ZIF-8@TiO₂ (KI) adsorption photocatalyst with good adsorption and photocatalytic properties. The samples were characterized by XRD, SEM, EDX, XPS, BET and UV-Vis. The photocatalytic efficiency of the material was obtained by photocatalytic tests. The results indicate that the doping with I inhibited the grain growth and reduced the crystallite size of TiO₂, reduced the band gap width and improved the utilization rate for light. TiO₂ (KI) was a single crystal of anatase titanium dioxide. The combination of ZIF-8 and TiO₂ (KI) improved the specific surface area and increased the reaction site. The ZIF-8@TiO₂ (KI) for Congo red was investigated to validate its photocatalytic performance. The optimal concentration of Congo red solution was 30 mg/L, and the amount of catalyst was proportional to the degradation efficiency. The degradation efficiency of ZIF-8@TiO₂ (5%KI) was 76.42%, after being recycled four times. Full article

(This article belongs to the Topic Materials and Catalysts for Pollutants and CO₂ Capture and Transformation)

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Figure 1

Figure 1
<p>(<b>a</b>) XRD patterns of TiO₂ doped with different amounts of I, (<b>b</b>) XRD patterns of TiO₂ (5%KI), ZIF-8, ZIF-8@TiO₂ (5%KI).</p> Full article ">Figure 1 Cont.
<p>(<b>a</b>) XRD patterns of TiO₂ doped with different amounts of I, (<b>b</b>) XRD patterns of TiO₂ (5%KI), ZIF-8, ZIF-8@TiO₂ (5%KI).</p> Full article ">Figure 2
<p>SEM (<b>a</b>) of ZIF-8; SEM (<b>b</b>–<b>d</b>) and TEM (<b>e</b>,<b>f</b>) of ZIF-8@TiO₂ (5%KI).</p> Full article ">Figure 3
<p>(<b>a</b>,<b>b</b>) ZIF-8@TiO₂ (5%KI) EDX diagram, (<b>c</b>) single element EDX diagram of ZIF-8@TiO₂ (5%KI).</p> Full article ">Figure 4
<p>ZIF-8@TiO₂ (5%KI) XPS analysis diagram. (<b>a</b>) XPS diagram of ZIF-8@TiO₂ (5%KI), (<b>b</b>) XPS diagram of N element, (<b>c</b>) XPS diagram of O element, (<b>d</b>) XPS diagram of Ti element, (<b>e</b>) XPS diagram of Zn element, (<b>f</b>) XPS diagram of I element.</p> Full article ">Figure 5
<p>(<b>a</b>) N₂-desorption diagram of TiO₂ (5%KI), (<b>b</b>) N₂-desorption diagram of ZIF-8, (<b>c</b>) N₂-desorption diagram of ZIF-8@TiO₂ (5%KI).</p> Full article ">Figure 6
<p>DRS diagram (<b>a</b>) and band gap width diagram (<b>b</b>).</p> Full article ">Figure 7
<p>Schematic of the photocatalytic mechanism of (<b>a</b>) TiO₂ (KI) and (<b>b</b>) ZIF-8@TiO₂ (5%KI).</p> Full article ">Figure 8
<p>(<b>a</b>) ZIF-8@TiO₂ (5%KI), TiO₂ (KI) and TiO₂ (350 °C) photocatalytic efficiency diagram, (<b>b</b>) kinetic equation of Congo red degradation, (<b>c</b>) effect of the initial concentration of Congo red on catalytic efficiency, and (<b>d</b>) effect of catalyst dosage on catalytic efficiency.</p> Full article ">Figure 8 Cont.
<p>(<b>a</b>) ZIF-8@TiO₂ (5%KI), TiO₂ (KI) and TiO₂ (350 °C) photocatalytic efficiency diagram, (<b>b</b>) kinetic equation of Congo red degradation, (<b>c</b>) effect of the initial concentration of Congo red on catalytic efficiency, and (<b>d</b>) effect of catalyst dosage on catalytic efficiency.</p> Full article ">

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